Process for the production of pure hydrofluoric acid from polluted fluorspars



- M. BUCHNER PROCESS FOR THE PRODUCTION OF PURE HYDROFLUORIC ACID FROM POLLUTED FLUORSPAHS Filed Jan. 5. 1926 Patented Feb. 5, 1929.

' STATES 1,701,225 PATENT OFFICE.

MAX BUCHNER, OF HANOVER-KLEEFELD, GERMANY, ASSIGNOR T ALBERT FRITZ MEYERHOFER, 0F ZURICH, SWITZERLAND.

PROCESS F03, THE PRODUCTION OF PURE HYDROFLUORIC 'ACID EROM' POLLUTED FLUORSPARS.

Application filed January 5, 1926, Serial No. 79,470, and in Germany January 16, 1925.

Hydrofluoric acid is obtained by treating fluorspar with acids. As the fluorspars to be bought in commerce are very seldom pure silicon fluoride is obtained by the treatment 5 with acids but the desired hydrofluoric acid 7 also produced necessitates, according to the normally known process, diflicult and trouble some refining proceedings.

This invention relates to the production of 10 hydrofluoric acid from impure fluorspars and it has for its object to transform the entire amount of fluor contained in the inital material into hydrofluoric acid, if desired, in a most economical manner. I

The invention consists in decomposing the gas mixture which has been liberated by means of acid from the impure fluorspar, and consisting of hydrofluoric acid and silicon fluoride and converting the hydrofluoric acid by means of fluorine compounds, on the one hand, into hydrofluoric salt, on the other hand, into free acid and in re-forming from the hydrofluoric salt obtained free hydroflu- 1 oric acid and/or the above stated desired fluorine compound.

According to the invention impure fluorspar is first decomposed, in a manner known per so, with an acid, for instance sulphuric acid, whereby silicon fluoride and hydrofluoric acid are liberated. This mixture is then treated with a fluoride, for instance barium.

fluoride. The silicon fluoride is bound, under formation of a complex fluoride, to the fluoride and, besides the complex fluoride, only hydrofluoric, acid remains. The complex fluoride is preferably decomposed by heat whereby the fluoride is recuperated which is required in the preceding step of the process.

1 At this separation silicon fluoride is obtained 40 from which hydrofluoric acid can also be obtained, The silicon fluoride is preferably used for the production of any metal compound prior to the converting ofits fluorine following equations a form of execution of this processis given, by wayofexample into hydroflouric acid. With the aid of the The silicon, which is present in the silicon fluoride obtained by the decomposition of the silico fluoride,,can be more or less converted into silica. With this object in view the silicon fluoride may be treated with bases. It is for instance added to a'solution of sodium hydroxide and in this manner silico fluoride, hydrofluoric acid and silica are obtained. The silico fluoride may be decomposed again by heat, so that a fluoride is obtained which may be utilized for the production of other combinations, Whilst the silicon fluoride, which has been liberated again, is worked up in another manner. The following equations represent such a working process and explain at the same time the production of nitrate by intermediary reactions.

CaF H SO,=CaSO QHF As silicon fluoride is continuously formed from the impure fluorspar, so that in the course of the process silicon fluorides are continuously formed anew, part of the silicon fluoride as well as the fluoride, from the reactions for the production of other combinations, may be utilized for there-building of silicon fluoride and in a'part of the cycle the production of other combinations, for instance, nitrates, phosphates, sodium carbonate, &c., with the production of sodium carbonate also ammonia and the like, can be car ried out continuously.

The new process permits of adaptation to the conditions determined by the composiv tion of the fluorspar utilized as initial material. If the fluorspar contains a large percentage of silica, e. g. silicon fluoride is formed in greater quantities during the acid decomposition of the fiuorsp-ar and, the silicon contained in the silicon fluoride will be transformed as far as possible into silica, or silicon fluorloacid is formed from the samein [addition to silica and, eventually also only silica. The reactions take place according to the followin g equations:

Highly voluminous silica very capable of reaction is obtained if the silicon fluoride is caused to act with steam alone or in presence of gases and vapours; The addition of gases or vapours of any kind serves for the purpose of lowering the concentration of the steam. Air is preferably used for this purpose with the aid of which the water is for instance atomized. The same effect, the formation of highly voluminous silica very capable of reaction, is obtained also when the decomposition of I silicon fluoride with water, which by the way leads to theformation of silicon fluoric acid, is carried out in presence of silica. The sili'- con fluoride is introduced into silico fluoric acid and produces in this manner highly con: centrated silico fluoric acid besides silica.

The production of silico fluoric acid from silicon fluoride and hydrofluoric acid may be effected in such a manner that the silicon fluoride is added directly to the gas mixture resulting from the acid decomposition of the fluorspar. There exist many possibilities of use for the silico fluoricacid obtained; it may the course of the process, as expr The reaction upon the gas mixture by meansof the silico fluoric acid salts is especially advisable if the proportion of silica in the fluorspar is very high. It in y. be mentioned that the insoluble fluorid rmed in d in the equations; for instance the calcium fluoride from which,-if desired, by means of acid pure hydrofluoric acid can be made, is obtained in a form which is extremely capable of reaction. The production of carbonates and hydroxides with utilization of the fluorides obtained in the process is especially important for the production of metal combinations. If an al.- kali fluoride has been obtained from the decomposition of the silico 'fluoride by heat it can be reacted upon with insoluble carbonates morass and hydroxides, whereby soluble carbonates and hydroxides are obtained.

QNaF CaCo =Na Go Cal QNa-F Ba (OH) =2Na@H+B aF There is also no difficulty in carrying out fluoiide/ The silico fluoride is brought to reaction for instance with a salt or with an acid as expressed by the following two equat1'onexamples The latter example shows already a manner of producing a special silico fluoric acid salt as is required for obtaining of a certain metal compound, in the present case of the lead arsenate. Other possibilities for the formation of the silico fluoric acid salts consist in that either the silico fluoric acid is built up by means of acid from an insoluble fluoride and silicon fluoride separated in the course of the process and in forming frpm this silico fluoric acid the desired salt, or by reacting with a fluoride, whether soluble or insoluble, and silicon fluoride or silica in presence of acid and of a salt. The salt which is introduced is a salt which contains the base to be bound to the silico fluoric acid.

If one works with silicon fluoride only small quantities of acid acting as contact substance -need be employed; In this case one may -work quite without acid. For the production of silico fluoric acid in the manner described the following equation may serve oar, SlT +H SO oaso,+ s iF,

dire ct formation of a silico fluoric acid salt from fluoride, silica, eventually salt and acids carrled out in the following manner:

The bracket (acid) indicates that 5 only small quantities of acid are required .as contact substance or that the acid maybe quite omitted.

With the production of hydrofluoric acid from impure fluorspar the production of any The several reactions,- which form the steps of the process, may be carried out at higher temperature and eventually under pressure. One may work further in concentrated solution or only with small quantities of solvents which are not suflicient for dissolving, or use salts in solid state.

The treatment of the impure fluorspar with acid, and the decomposition of the gas mixture into free acid and a salt is preferably carried out in a heatable and rotatable cylinder with two chambers. The first chamber is charged continuously with the mixture of fluorspar and acid, and the residue is removed from time to time.

The partition which separates the two chambers is perforated so that'the gas mixture generated,

. consisting of hydrofluoric acid and silicon time.

fluoride, can flowfover into the second chamber. This second chamber is preferably charged, in using insuflicient quantities of solvents, with the fluoride or silico fluoride designed for the treatment of the. gas mix- According to the manner in which the heating of the rotatable cylinder is regulated the free acid separated or formed in the second chamber can be delivered from the chamber in gaseous state or withdrawn from the chamber, together with'thesa'lt which has been formed, in dissolved state. The

emptying of the second chamber is carried out independently of the first chamber and at any desired time, i

The accompanying drawing shows such a cylinder in longitudinal section. a and b are the two chambers, c is the perforated partition, 0? is the supply tube for the mixture of fluorspar and acid. The salt designed for the treatment of the gas mixture-is admitted through c, and 7 serves as outlet for the pure hydrofluoric acid or for the silico hydrofluoric'acid in gaseous state. At 9 traps for the emptying of the chamber a are arranged. it are the emptying traps for thechamber bu Baflle plates or stirrers z'may be arranged in the chamber Z) on the inlet pipe at and designed to force the gas. mixture to flowto the actually lowest portion of the rotating cylinder.

Thefluorspar and acid mixture is supplied pipe d. The resultiiliag t e gaseous reaction products pass through solid reaction product, mainly calcium salt,

is discharged through the openings g.

In chamber Z) the gaseous hydrofluoric acid and silicon fluoride is supplied with a simple fluoride or a complex fluoride through pipe 0, to bind the silicon fluoride asa complex fluoride, which latter is discharged through openings h, while the pure hydrofluoric acid passes out through pipe I claim: I

1. The art of producing pure hydrofluoric acid from impure fluorspar, which comprises reacting on impure fluorspar with an acid capable of forming a gas mixture of hydrofluoric acid and silicon. fluoride, reacting on said mixture with a fluorine compound to form a fluoride, and reacting on the fluoride so formed with a compound capable of forming 'a fluorinecompound forv reaction on the gasmixture and a tree fluoric acid.

silicon fluoride with a suitable substance to produce a fluoric acid.

3. The art of producing pure fluoric acid from impure fluorspar, acting on impure fluorspar With an acid capable of forming a 'gas'mixture of hydrowhich comprises refluoric acid and silicon fluoride, binding the silicon fluoride to asimple fluoride to form a complex fluoride, decomposing the complex fluoride into simple fluoride for reaction with said gas mixture and reacting on the silicon fluoride with a reagent to form a fluoric acid.

4. The art of producing a pure fluoric acid,

which comprises reacting upon impure flllOl".

spar with an acid capable of forming a gas mixture of hydrofluoric acid and silicon fluoride, reacting on the mixture with a complex fluoride to form a simple fluoride and a complex fluoric acid, forming a soluble fluoride of such acid, reacting on such fluoride with a reagent capable of forming an insoluble complex fluoride and a soluble salt, recovering silicon fluoride from the complex salt and reacting on the latter with a simple fluoride to form a complexfluoride for re action with the gas mixture.

5. The artof making a pure fluoric acid from impure fluorspar, whichcompriees reacting thereonwith an acid capable offerining "a gas mixture of hydrofluoric acid and silicon fluoride, reacting upon the mixture fluorideand silico-fluoricacid, and reacting on the latter with mineral acid to produce 139 pure hydrofluoric acid and silicon fluoride, re-

forming the silico-fluoride from the silicon fluoride for treatment of the gas mixture and same in the presence of heat to form a gas mixture of hydrofluoric acid and silicon fluoride, treating the gas mixture with a fluoride to form a complexfluoride and hydrofluoric acid, converting the complex fluoride into the fluoride for the treatment of the gas mixtureand silicon fluoride, and reacting upon the silicon fluoride wit-ha reagent capable of forming a fluoric acid.

7. The art of produc ng pure hydrofluoric acid from fluorspar containing silicon as. an

impurity, which comprises reacting on such impure fluorspar with a mineral acid to form a gas mixture of hydrofluoric acid and silicon fluoride, binding the silicon fluoride content of the mixture by' another simple metal fluoride to a complex fluoride and recovering pure hydrofluoric acid, decomposing the complex fluoride into a simple metal fluoride and silicon fluoride, reacting on the silicon fluoride with a suitable reagent to separate silicon and bind the fluorine toanother base, and reacting on the resulting fluoride with suitable substances to liberate the fluorine heretofore bound to silicon as hydrofluoric acid.

lln testimony that I claim the foregoing as my invention, it have signed my name;

DR. MAX BUGHNER. 

